A diamond body, including a free-standing (stand-alone) CVD (chemical vapor deposited) diamond film, is useful in a variety of contexts, such as a heat-spreading submount for a semiconductor laser chip or a semiconductor integrated circuit chip. Presently available free-standing CVD films typically exhibit an undesirably relatively rough (large grain) top surface and a relatively smooth (small grain) but undesirably relatively low thermal conductivity bottom surface. The thermal conductivity thus has a gradient going from the top to the bottom surface. As described in a paper by J. E. Graebner et al., published in Applied Physics Letters, Vol. 60, pp. 1576-1578 (Mar. 30, 1992), entitled "Unusually High Thermal Conductivity in Diamond Films," this gradient is believed to be attributable to a cone-shaped columnar crystal structure of the film, the cones having their vertices located at or near the bottom surface of the film at its interface with an underlying substrate on which the film has been grown. Those of the columnar cones that extend all the way to the top surface of the film have less sub-structure than those that do not. This type of microstructure causes an undesirably low average transverse (spreading) thermal conductivity of the diamond film at its bottom regions, as well as poor thermal contact with, for example, a laser chip located on the rough top surface of the diamond film. Likewise, there can arise a problem of poor thermal contact of the rough bottom surface of the diamond film with a metallic or ceramic heatsinking mount. Thus, removal of a thickness of diamond material from its top and bottom surfaces is desirable.
The paper "Massive thinning of diamond films by a diffusion process," authored by S. Jin et al, and published in Applied Physics Letters, Vol. 60, pp. 1948-1950 (20 Apr. 1992) teaches a technique for removing diamond material simultaneously from top and bottom regions of a free-standing CVD diamond film, in order to smoothen the top surface and at the same time to remove undesirably low thermal conductivity material located at the bottom surface. In accordance with that technique, the free-standing diamond film is sandwiched between a pair of thin iron sheets (foils) and heat treated at 900.degree. C. under a constant stress for a time duration of 48 hours in an argon gas atmosphere. Although the technique is useful for its intended purpose, namely, thinning the CVD diamond film by approximately 100 .mu.m (50 .mu.m on each main face), a shorter time duration would be desirable, especially from an economic standpoint. Furthermore, the required application of high pressure (typically approximately 20 MPa for the case of etching with iron), to ensure good contact between the solid metal and diamond surfaces during heat treatment, is not desirable from an industrial point of view. Therefore, a faster and lower-pressure method of removing (diamond) material from a face of diamond body is desirable, at little or no sacrifice of surface smoothness (if not gain in surface smoothness).